Common hot water systems typically comprise at least one tank which stores water and is associated with a heating system, such as an electric heating element, a gas heater, a heat pump, or a solar heater, which heats the water for storage in the tank. The heating system may be incorporated into the tank, heating the water internally of the tank, or may be in fluid communication with the tank, heating the water externally of the tank and feeding the heated water into the tank.
In both domestic and industrial hot water systems, the hot water storage tank is typically constructed primarily of metal, such as steel. Over time the metal corrodes leading to pollution of the water in the tank in the short term and ultimately, leading to failure of the tank in the medium term. Due to corrosion and operational stresses, many hot water storage tanks need to be replaced after only a few years of use, resulting in a recurring cost to the consumer and a significant amount of waste material when a disused tank is discarded.
Common hot water heater tanks are manufactured from welded steel having a corrosion resistant lining of vitreous enamel or copper applied after fabrication, a complex and expensive manufacturing process. The high level, and cyclic nature, of the stresses applied to the tank in operation, due to fluctuations in both temperature and pressure, cause cracking of the lining, particularly at seams between the various components of the fabricated shell. Additionally, over time, with the effect of higher temperatures the vitreous enamel will ultimately dissolve into the water. Where the enamelling process has not been successful during manufacture, this dissolution can be accelerated and lead to premature failure of the tank.
Accordingly, such hot water heater tanks commonly fail by corrosion, frequently after less than ten or twelve years' service. While anodic protection can assist in restraining the corrosion process, it is reliant on the provision of appropriate maintenance by the consumer, which is frequently not provided. The corrosion problem can be addressed by the use of stainless steel however this has the disadvantage of substantially increasing the raw material costs and can only be successfully used in areas where the potable water quality is maintained within relatively tight parameters.
Steel manufacture itself is highly energy intensive and creates a large carbon footprint, making it an unattractive construction material from an environmental standpoint. As a result, the environmental credentials of steel hot water tanks are poor, since the overall manufacturing process involves a large amount of energy use and creates a large carbon footprint.
Once manufactured, metal tanks are also quite heavy and cumbersome, making them difficult to handle and expensive to transport. Heavy and cumbersome tanks are difficult for a tradesperson to install and often require a team of installers and/or machinery to lift and install the tanks.
While metal tanks have good strength characteristics, metals are particularly good conductors of heat. In order to satisfy the statutory maximum permissible heat loss requirements, it is therefore necessary for a metal tank to have thicker insulation than would be the case if the tank was constructed of a poor heat conducting material. Thicker insulation has the disadvantages of greater weight, size and cost of the finished water tank.
Polymer resin moulded water tanks, such as polyethylene rainwater tanks, are commonly used to store water and chemicals at ambient temperatures and pressures. However, these tanks are not suitable for storing heated and pressurised water such as the hot water in a domestic or commercial/industrial hot water system. Typical polymer tanks would deform and ultimately fail, due to the operating temperatures, pressures, stresses and strains to which a typical hot water tank is subjected in ordinary use.
Thus, a need exists to provide a lightweight, strong, durable and energy saving storage solution for hot water systems.
The above discussion of the prior art in the background of the invention is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.